-- change_requests: one row links project/workspace/(requirement|issue)/source+target
-- branch with a review verdict + CI state + the external (Gitea) PR id. This is
-- the server-side merge gate: an agent opens a reviewable PR; a human approves
-- via the web before merge_pull_request can succeed.
--
-- number is a per-project sequence (max(number)+1 within project_id), mirroring
-- requirements/issues. Columns are appended in physical order; sqlc SELECT/RETURNING
-- column order must match this order (sqlc 列序约定，见 migrations/0012 comment)。
CREATE TABLE change_requests (
  id               UUID PRIMARY KEY,
  project_id       UUID NOT NULL REFERENCES projects(id)     ON DELETE CASCADE,
  workspace_id     UUID NOT NULL REFERENCES workspaces(id)   ON DELETE CASCADE,
  requirement_id   UUID     REFERENCES requirements(id)      ON DELETE SET NULL,
  issue_id         UUID     REFERENCES issues(id)            ON DELETE SET NULL,
  number           INT  NOT NULL,
  title            TEXT NOT NULL,
  description      TEXT NOT NULL DEFAULT '',
  source_branch    TEXT NOT NULL,
  target_branch    TEXT NOT NULL,
  state            TEXT NOT NULL DEFAULT 'open'    CHECK (state IN ('open','merged','closed')),
  review_verdict   TEXT NOT NULL DEFAULT 'pending' CHECK (review_verdict IN ('pending','approved','changes_requested','rejected')),
  ci_state         TEXT NOT NULL DEFAULT 'unknown' CHECK (ci_state IN ('unknown','pending','success','failure')),
  provider         TEXT NOT NULL DEFAULT 'gitea',
  external_id      BIGINT,
  external_url     TEXT NOT NULL DEFAULT '',
  merge_commit_sha TEXT NOT NULL DEFAULT '',
  reviewed_by      UUID     REFERENCES users(id)             ON DELETE SET NULL,
  reviewed_at      TIMESTAMPTZ,
  created_by       UUID NOT NULL REFERENCES users(id)        ON DELETE RESTRICT,
  merged_at        TIMESTAMPTZ,
  created_at       TIMESTAMPTZ NOT NULL DEFAULT now(),
  updated_at       TIMESTAMPTZ NOT NULL DEFAULT now(),
  UNIQUE (project_id, number)
);

CREATE INDEX idx_change_requests_workspace ON change_requests(workspace_id);
CREATE INDEX idx_change_requests_open ON change_requests(workspace_id) WHERE state = 'open';