/* ═══════════════════════════════════════════════════════════════
   ADMIN CRUD ENGINE

   Reads a descriptor from admin-schema.js and does the SQL. No
   entity names appear in this file.

   Writes run inside tx() so a parent, its side table, and every
   child collection either all land or none do. Children are
   replaced wholesale rather than diffed: the client sends the list
   it wants to exist, the engine deletes and reinserts in array
   order, and sort_order becomes the index. That makes drag-to-
   reorder free and removes a whole class of "which row is this"
   bugs, at the cost of churning autoincrement ids — which is fine
   precisely because nothing references them.

   A column that isn't present in the payload at all is left out of
   the statement entirely, so the table's DEFAULT applies on insert
   and the existing value survives on update. A column present but
   empty ("" or null) is an explicit clear and writes NULL. The
   difference matters: sending NULL for every unmentioned column is
   what turns a missing form field into a NOT NULL constraint
   failure instead of a default.
   ═══════════════════════════════════════════════════════════════ */

import { tx } from "./db.js";

export class HttpError extends Error {
  constructor(status, message, fields) {
    super(message);
    this.status = status;
    this.fields = fields;
  }
}

const SLUG = /^[a-z0-9][a-z0-9-]{0,63}$/;
const ISO_DATE = /^\d{4}-\d{2}-\d{2}$/;
const CLOCK_TIME = /^([01]\d|2[0-3]):[0-5]\d$/;

/* Not a value the caller can ever send, so it can mean "leave this
   column out of the statement" without colliding with real data. */
const OMIT = Symbol("omit");

/* ── Coercion ──────────────────────────────────────────────────
     SQLite STRICT tables reject a type mismatch at the wall, but
     the error it throws is unreadable. Everything is converted and
     checked here so failures come back as named fields.
   ───────────────────────────────────────────────────────────── */

function coerceValue(column, raw, errors, prefix = "") {
  const key = `${prefix}${column.name}`;

  // Absent from the payload. Fall back to the descriptor default
  // if it declares one, otherwise let the column's own DEFAULT do
  // the work — which needs the column omitted, not nulled.
  if (raw === undefined) {
    if (column.default !== undefined) return column.default;
    if (column.required) errors[key] = "Required.";
    return OMIT;
  }

  // Before the blank check: an unchecked box legitimately arrives
  // as false, "", or null, and all of those mean 0, not NULL.
  if (column.type === "bool") {
    return raw === true || raw === 1 || raw === "1" || raw === "true" ? 1 : 0;
  }

  if (raw === null || raw === "") {
    if (column.required) {
      errors[key] = "Required.";
      return null;
    }
    // The table refuses NULL but declares a default: clearing the
    // field means "use the default", not "write NULL".
    if (column.notNullable) return OMIT;
    return null;
  }

  switch (column.type) {
    case "int": {
      const n = Number(raw);
      if (!Number.isInteger(n)) errors[key] = "Must be a whole number.";
      return Number.isInteger(n) ? n : null;
    }
    case "real": {
      const n = Number(raw);
      if (!Number.isFinite(n)) errors[key] = "Must be a number.";
      return Number.isFinite(n) ? n : null;
    }
    case "enum": {
      const value = String(raw);
      if (!column.values.includes(value)) {
        errors[key] = `Must be one of: ${column.values.join(", ")}.`;
        return null;
      }
      return value;
    }
    case "date": {
      const value = String(raw).trim();
      if (!ISO_DATE.test(value)) errors[key] = "Use YYYY-MM-DD.";
      return ISO_DATE.test(value) ? value : null;
    }
    case "time": {
      // <input type="time"> sends HH:MM, or HH:MM:SS when a step
      // asks for seconds. Nothing here does, so seconds are dropped.
      const value = String(raw).trim().slice(0, 5);
      if (!CLOCK_TIME.test(value)) errors[key] = "Use HH:MM, 24-hour.";
      return CLOCK_TIME.test(value) ? value : null;
    }
    default: {
      const value = String(raw).trim();
      return value === "" ? null : value;
    }
  }
}

function coerceRow(columns, data, { prefix = "" } = {}) {
  const errors = {};
  const values = {};
  for (const column of columns) {
    const value = coerceValue(column, data?.[column.name], errors, prefix);
    if (value !== OMIT) values[column.name] = value;
  }
  return { values, errors };
}

const applies = (gate, row) => !gate || row[gate.column] === gate.value;

/* ── Read ────────────────────────────────────────────────────── */

export function listRows(db, entity, query = {}) {
  const { columns, filters, search, order } = entity.list;

  const where = [];
  const params = [];

  for (const name of filters) {
    const value = query[name];
    if (value === undefined || value === "" || value === "all") continue;
    where.push(`${name} = ?`);
    params.push(value);
  }

  if (query.q) {
    const term = `%${String(query.q).slice(0, 100)}%`;
    where.push(`(${search.map((c) => `${c} LIKE ?`).join(" OR ")})`);
    params.push(...search.map(() => term));
  }

  const limit = Math.min(Number(query.limit) || 200, 500);

  const rows = db
    .prepare(
      `SELECT ${columns.join(", ")}
         FROM ${entity.table}
        ${where.length ? `WHERE ${where.join(" AND ")}` : ""}
        ORDER BY ${order}
        LIMIT ?`,
    )
    .all(...params, limit);

  return { rows, total: rows.length };
}

export function readRow(db, entity, rawId) {
  const id = normalizeId(entity, rawId);
  const row = db
    .prepare(`SELECT * FROM ${entity.table} WHERE ${entity.idColumn} = ?`)
    .get(id);

  if (!row) throw new HttpError(404, "Not found.");

  for (const ext of entity.extensions ?? []) {
    row[ext.key] = readExtension(db, ext, id);
  }

  for (const child of entity.children ?? []) {
    row[child.key] = readChildren(db, child, id);
  }

  return row;
}

/* A 1:1 side table is found one of two ways. `idColumn` is the
   original: the side table's key IS the parent's id, which is how
   regions and person_private work. `owner` is the same block children
   already use — a foreign key column plus an optional kind discriminator
   — and it exists because a timeline entry is keyed by (ref_kind,
   ref_id) rather than by the event's own slug. Same upsert either way;
   only the WHERE differs. */
function extensionWhere(ext, id) {
  if (!ext.owner) return { sql: `${ext.idColumn} = ?`, params: [id] };
  const where = [`${ext.owner.column} = ?`];
  const params = [id];
  if (ext.owner.kindColumn) {
    where.push(`${ext.owner.kindColumn} = ?`);
    params.push(ext.owner.kindValue);
  }
  return { sql: where.join(" AND "), params };
}

function readExtension(db, ext, id) {
  const { sql, params } = extensionWhere(ext, id);
  return db.prepare(`SELECT * FROM ${ext.table} WHERE ${sql}`).get(...params) ?? null;
}

function readChildren(db, child, ownerId) {
  const where = [`${child.owner.column} = ?`];
  const params = [ownerId];

  if (child.owner.kindColumn) {
    where.push(`${child.owner.kindColumn} = ?`);
    params.push(child.owner.kindValue);
  }

  const rows = db
    .prepare(
      `SELECT * FROM ${child.table}
        WHERE ${where.join(" AND ")}
        ORDER BY ${child.order}`,
    )
    .all(...params);

  for (const child2 of child.children ?? []) {
    for (const row of rows) {
      row[child2.key] = db
        .prepare(
          `SELECT * FROM ${child2.table}
            WHERE ${child2.owner.column} = ?
            ORDER BY ${child2.order}`,
        )
        .all(row.id);
    }
  }

  return rows;
}

/* ── Write ───────────────────────────────────────────────────── */

/* An entity whose id is an autoincrement integer is addressed by a
   number, and a number arriving from a URL segment is a string. Every
   comparison against the id column goes through here so the two can't
   drift apart. */
export function normalizeId(entity, id) {
  if (entity.idKind !== "auto") return id;
  const n = Number(id);
  if (!Number.isInteger(n)) throw new HttpError(404, "Not found.");
  return n;
}

export function createRow(db, entity, payload) {
  // idKind "auto": the table assigns the id, so there is nothing to
  // validate, nothing to check for collisions, and nothing for the
  // client to have sent. Timeline entries use this — they have no
  // natural name to slug, and one gets created every time somebody
  // ticks a checkbox on an event.
  const auto = entity.idKind === "auto";
  const id = auto
    ? null
    : String(payload?.[entity.idColumn] ?? "").trim().toLowerCase();

  if (!auto) {
    if (entity.idKind === "slug" && !SLUG.test(id)) {
      throw new HttpError(422, "Validation failed", {
        [entity.idColumn]: "Lowercase letters, numbers and hyphens only.",
      });
    }

    const exists = db
      .prepare(`SELECT 1 FROM ${entity.table} WHERE ${entity.idColumn} = ?`)
      .get(id);
    if (exists) {
      throw new HttpError(422, "Validation failed", {
        [entity.idColumn]: "Already taken.",
      });
    }
  }

  const { values, errors } = coerceRow(entity.columns, payload);
  if (Object.keys(errors).length) {
    throw new HttpError(422, "Validation failed", errors);
  }

  let newId = id;

  wrapDbErrors(() =>
    tx(db, () => {
      if (auto) {
        const names = Object.keys(values);
        // Every column omitted is legitimate here: a blank entry that
        // takes all its defaults. INSERT INTO t () VALUES () is not
        // valid SQL, so that case needs DEFAULT VALUES.
        const result = names.length
          ? db
              .prepare(
                `INSERT INTO ${entity.table} (${names.join(", ")})
                 VALUES (${names.map(() => "?").join(", ")})`,
              )
              .run(...Object.values(values))
          : db.prepare(`INSERT INTO ${entity.table} DEFAULT VALUES`).run();
        // better-sqlite3 and node:sqlite disagree about BigInt here.
        newId = Number(result.lastInsertRowid);
      } else {
        const names = [entity.idColumn, ...Object.keys(values)];
        db.prepare(
          `INSERT INTO ${entity.table} (${names.join(", ")})
           VALUES (${names.map(() => "?").join(", ")})`,
        ).run(id, ...Object.values(values));
      }

      writeExtensions(db, entity, newId, payload, values);
      writeChildren(db, entity, newId, payload, values);
    }),
  );

  return readRow(db, entity, newId);
}

export function updateRow(db, entity, rawId, payload) {
  const id = normalizeId(entity, rawId);
  const current = db
    .prepare(`SELECT * FROM ${entity.table} WHERE ${entity.idColumn} = ?`)
    .get(id);
  if (!current) throw new HttpError(404, "Not found.");

  // Optimistic concurrency. The client echoes back the updated_at
  // it loaded; anything else means someone saved in between.
  if (entity.concurrency) {
    const seen = payload?.[entity.concurrency];
    if (!seen) {
      throw new HttpError(400, `Missing ${entity.concurrency}.`);
    }
    if (seen !== current[entity.concurrency]) {
      throw new HttpError(
        409,
        "Someone else saved this while you were editing. Reload to see their version.",
      );
    }
  }

  const { values, errors } = coerceRow(entity.columns, payload);
  if (Object.keys(errors).length) {
    throw new HttpError(422, "Validation failed", errors);
  }

  // An unsent column keeps its stored value, so the gates below
  // have to read the merged row, not just what came in.
  const merged = { ...current, ...values };

  wrapDbErrors(() =>
    tx(db, () => {
      const sets = Object.keys(values).map((name) => `${name} = ?`);
      if (sets.length) {
        db.prepare(
          `UPDATE ${entity.table} SET ${sets.join(", ")}
            WHERE ${entity.idColumn} = ?`,
        ).run(...Object.values(values), id);
      }

      writeExtensions(db, entity, id, payload, merged);
      writeChildren(db, entity, id, payload, merged);
    }),
  );

  return readRow(db, entity, id);
}

export function deleteRow(db, entity, rawId) {
  const id = normalizeId(entity, rawId);
  const result = wrapDbErrors(() =>
    db.prepare(`DELETE FROM ${entity.table} WHERE ${entity.idColumn} = ?`).run(id),
  );
  if (result.changes === 0) throw new HttpError(404, "Not found.");
}

/* ── Write helpers ───────────────────────────────────────────── */

function writeExtensions(db, entity, id, payload, parentValues) {
  for (const ext of entity.extensions ?? []) {
    if (!applies(ext.when, parentValues)) {
      // The gate closed — the kind changed away from this side
      // table, or a checkbox was unticked — so its row (and anything
      // cascading off it) goes.
      const gone = extensionWhere(ext, id);
      db.prepare(`DELETE FROM ${ext.table} WHERE ${gone.sql}`).run(...gone.params);
      continue;
    }

    const { values, errors } = coerceRow(ext.columns, payload[ext.key] ?? {}, {
      prefix: `${ext.key}.`,
    });
    if (Object.keys(errors).length) {
      throw new HttpError(422, "Validation failed", errors);
    }

    if (ext.touch) values.updated_at = new Date().toISOString().replace("T", " ").slice(0, 19);

    // The owning columns come first, then whatever the form sent.
    const ownNames = [];
    const ownParams = [];
    if (ext.owner) {
      ownNames.push(ext.owner.column);
      ownParams.push(id);
      if (ext.owner.kindColumn) {
        ownNames.push(ext.owner.kindColumn);
        ownParams.push(ext.owner.kindValue);
      }
    } else {
      ownNames.push(ext.idColumn);
      ownParams.push(id);
    }

    const names = [...ownNames, ...Object.keys(values)];
    const sets = Object.keys(values).map((n) => `${n} = excluded.${n}`);

    // What makes this row the same row on a second save. Defaults to
    // the id column; an owned extension declares the unique index its
    // owning columns form.
    const conflict = ext.conflict ?? ownNames;

    // Upsert rather than delete-and-insert: deleting a regions row
    // would cascade its region_areas away underneath us, and deleting
    // a timeline row would take its people with it. With every
    // optional column omitted there is nothing to set, so the
    // conflict clause has to degrade to DO NOTHING or the SQL is
    // syntactically invalid.
    db.prepare(
      `INSERT INTO ${ext.table} (${names.join(", ")})
       VALUES (${names.map(() => "?").join(", ")})
       ON CONFLICT(${conflict.join(", ")}) ${
         sets.length ? `DO UPDATE SET ${sets.join(", ")}` : "DO NOTHING"
       }`,
    ).run(...ownParams, ...Object.values(values));
  }
}

function isBlankChildRow(child, raw) {
  if (!raw || typeof raw !== "object") return true;

  for (const column of child.columns) {
    const value = raw[column.name];
    if (value === undefined || value === null || value === "") continue;
    // An unchecked box is the default state of a new row, not input.
    if (
      column.type === "bool" &&
      (value === false || value === 0 || value === "0" || value === "false")
    ) {
      continue;
    }
    return false;
  }

  for (const child2 of child.children ?? []) {
    const nested = raw[child2.key];
    if (Array.isArray(nested) && nested.some((item) => !isBlankChildRow(child2, item))) {
      return false;
    }
  }

  return true;
}

function keyedDbErrors(prefix, fn) {
  try {
    return fn();
  } catch (err) {
    if (err instanceof HttpError) throw err;
    const notNull = /NOT NULL constraint failed: \w+\.(\w+)/.exec(String(err.message ?? ""));
    if (notNull) {
      throw new HttpError(422, "Validation failed", {
        [`${prefix}${notNull[1]}`]: "Required.",
      });
    }
    throw err;
  }
}

function writeChildren(db, entity, id, payload, parentValues) {
  for (const child of entity.children ?? []) {
    if (!applies(child.when, parentValues)) {
      deleteChildren(db, child, id);
      continue;
    }
    if (payload[child.key] === undefined) continue; // not sent, not touched

    deleteChildren(db, child, id);

    const incoming = Array.isArray(payload[child.key]) ? payload[child.key] : [];

    // index is the row's place in what the client sent, so a
    // validation error still points at the row the user is looking
    // at. position counts only the rows that survive, so dropping a
    // blank in the middle doesn't leave a gap in sort_order.
    const rows = incoming
      .map((raw, index) => ({ raw, index }))
      .filter(({ raw }) => child.allowBlank || !isBlankChildRow(child, raw));

    rows.forEach(({ raw, index }, position) => {
      const { values, errors } = coerceRow(child.columns, raw, {
        prefix: `${child.key}.${index}.`,
      });
      if (Object.keys(errors).length) {
        throw new HttpError(422, "Validation failed", errors);
      }

      const names = [child.owner.column, ...Object.keys(values)];
      const params = [id, ...Object.values(values)];

      if (child.owner.kindColumn) {
        names.push(child.owner.kindColumn);
        params.push(child.owner.kindValue);
      }
      for (const [column, from] of Object.entries(child.owner.inherit ?? {})) {
        if (names.includes(column)) continue;
        names.push(column);
        params.push(parentValues[from] ?? id);
      }
      if (child.order === "sort_order" && !names.includes("sort_order")) {
        names.push("sort_order");
        params.push(position);
      }

      const result = keyedDbErrors(`${child.key}.${index}.`, () =>
        db
        .prepare(
          `INSERT INTO ${child.table} (${names.join(", ")})
           VALUES (${names.map(() => "?").join(", ")})`,
        )
        .run(...params),
      );

      for (const child2 of child.children ?? []) {
        const incomingNested = Array.isArray(raw[child2.key]) ? raw[child2.key] : [];
        const nested = incomingNested
          .map((rawItem, i) => ({ rawItem, i }))
          .filter(({ rawItem }) => child2.allowBlank || !isBlankChildRow(child2, rawItem));

        nested.forEach(({ rawItem, i }, nestedPosition) => {
          const item = coerceRow(child2.columns, rawItem, {
            prefix: `${child.key}.${index}.${child2.key}.${i}.`,
          });
          if (Object.keys(item.errors).length) {
            throw new HttpError(422, "Validation failed", item.errors);
          }

          const itemNames = [child2.owner.column, ...Object.keys(item.values)];
          const itemParams = [result.lastInsertRowid, ...Object.values(item.values)];
          if (!itemNames.includes("sort_order")) {
            itemNames.push("sort_order");
            itemParams.push(nestedPosition);
          }

          db.prepare(
            `INSERT INTO ${child2.table} (${itemNames.join(", ")})
             VALUES (${itemNames.map(() => "?").join(", ")})`,
          ).run(...itemParams);
        });
      }
    });
  }
}

function deleteChildren(db, child, ownerId) {
  if (child.owner.kindColumn) {
    db.prepare(
      `DELETE FROM ${child.table}
        WHERE ${child.owner.column} = ? AND ${child.owner.kindColumn} = ?`,
    ).run(ownerId, child.owner.kindValue);
  } else {
    db.prepare(`DELETE FROM ${child.table} WHERE ${child.owner.column} = ?`).run(
      ownerId,
    );
  }
}

/* SQLite's constraint messages are accurate and unreadable. Turn
   the ones that users actually cause into something actionable,
   and name the column wherever the message carries it — a missing
   field is the client's problem to fix, not a 500.

   The descriptor and the schema agreeing (see admin-schema-sync.js)
   should stop most of these arriving. This is the backstop for the
   cases it can't see: partial indexes, triggers, CHECK constraints. */
function wrapDbErrors(fn) {
  try {
    return fn();
  } catch (err) {
    if (err instanceof HttpError) throw err;
    const message = String(err.message ?? "");

    const notNull = /NOT NULL constraint failed: \w+\.(\w+)/.exec(message);
    if (notNull) {
      throw new HttpError(422, "Validation failed", {
        [notNull[1]]: "Required.",
      });
    }

    const unique = /UNIQUE constraint failed: (.+)/.exec(message);
    if (unique) {
      const columns = unique[1]
        .split(",")
        .map((part) => part.trim().split(".")[1])
        .filter(Boolean);
      if (columns.length === 1) {
        throw new HttpError(422, "Validation failed", {
          [columns[0]]: "Already taken.",
        });
      }
      throw new HttpError(422, "That combination already exists.");
    }

    if (message.includes("FOREIGN KEY")) {
      throw new HttpError(
        422,
        "Something references a row that doesn't exist, or is still referenced elsewhere.",
      );
    }

    const check = /CHECK constraint failed: (\w+)/.exec(message);
    if (check) {
      throw new HttpError(422, `A value was rejected by the "${check[1]}" rule.`);
    }

    // The polymorphic tables stand in for a foreign key with a
    // BEFORE INSERT trigger, and a trigger's RAISE(ABORT) matches none
    // of the patterns above — so without this, pointing a content
    // block, link or timeline entry at a row that isn't there is a 500
    // rather than something the form can show.
    const ghost = /^(\w+): no such (\w+)$/.exec(message);
    if (ghost) {
      throw new HttpError(
        422,
        `That points at ${/^[aeiou]/i.test(ghost[2]) ? "an" : "a"} ${ghost[2]} that doesn't exist.`,
      );
    }

    throw err;
  }
}