-- Migration 001: Initial schema
-- Creates all tables for the pixa caching image proxy

-- Source images, one row per source URL
-- Files stored at: cache/sources/<ab>/<cd>/<source_key>, where source_key
-- is the SHA-256 of the source's host, path and query
CREATE TABLE IF NOT EXISTS source_content (
    source_key TEXT PRIMARY KEY,
    content_type TEXT NOT NULL,
    size_bytes INTEGER NOT NULL,
    last_accessed_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
);
CREATE INDEX IF NOT EXISTS idx_source_content_last_accessed
    ON source_content(last_accessed_at);

-- Processed variant blobs
-- Files stored at: cache/variants/<ab>/<cd>/<cache_key>. Tracked here
-- (like source content blobs above) so total cache usage is known
-- without a directory scan, and so LRU eviction has a timestamp to order
-- on. A cache hit does not read this table: it takes the content type
-- from the file's first bytes, and its last_accessed_at is written
-- later, in a batch.
CREATE TABLE IF NOT EXISTS variant_content (
    cache_key TEXT PRIMARY KEY,
    size_bytes INTEGER NOT NULL,
    last_accessed_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
);
CREATE INDEX IF NOT EXISTS idx_variant_content_last_accessed
    ON variant_content(last_accessed_at);

-- Total cache usage: the sum of size_bytes over source_content and
-- variant_content, kept by the triggers below in the same statement
-- that adds, removes or resizes a row, so eviction reads this one row
-- instead of summing both tables. Each trigger also adds one to
-- change_count; the reconciliation pass, which sums both tables a page
-- at a time, corrects total_size_bytes only if change_count did not
-- move while it summed.
CREATE TABLE IF NOT EXISTS cache_usage (
    id INTEGER PRIMARY KEY CHECK (id = 1),
    total_size_bytes INTEGER NOT NULL DEFAULT 0,
    change_count INTEGER NOT NULL DEFAULT 0
);
INSERT OR IGNORE INTO cache_usage (id) VALUES (1);

CREATE TRIGGER IF NOT EXISTS source_content_usage_insert
AFTER INSERT ON source_content
BEGIN
    UPDATE cache_usage
    SET total_size_bytes = total_size_bytes + NEW.size_bytes,
        change_count = change_count + 1
    WHERE id = 1;
END;

CREATE TRIGGER IF NOT EXISTS source_content_usage_delete
AFTER DELETE ON source_content
BEGIN
    UPDATE cache_usage
    SET total_size_bytes = total_size_bytes - OLD.size_bytes,
        change_count = change_count + 1
    WHERE id = 1;
END;

CREATE TRIGGER IF NOT EXISTS source_content_usage_update
AFTER UPDATE OF size_bytes ON source_content
BEGIN
    UPDATE cache_usage
    SET total_size_bytes = total_size_bytes - OLD.size_bytes + NEW.size_bytes,
        change_count = change_count + 1
    WHERE id = 1;
END;

CREATE TRIGGER IF NOT EXISTS variant_content_usage_insert
AFTER INSERT ON variant_content
BEGIN
    UPDATE cache_usage
    SET total_size_bytes = total_size_bytes + NEW.size_bytes,
        change_count = change_count + 1
    WHERE id = 1;
END;

CREATE TRIGGER IF NOT EXISTS variant_content_usage_delete
AFTER DELETE ON variant_content
BEGIN
    UPDATE cache_usage
    SET total_size_bytes = total_size_bytes - OLD.size_bytes,
        change_count = change_count + 1
    WHERE id = 1;
END;

CREATE TRIGGER IF NOT EXISTS variant_content_usage_update
AFTER UPDATE OF size_bytes ON variant_content
BEGIN
    UPDATE cache_usage
    SET total_size_bytes = total_size_bytes - OLD.size_bytes + NEW.size_bytes,
        change_count = change_count + 1
    WHERE id = 1;
END;

-- Negative cache: source URLs whose fetch failed with an upstream error
-- status, or whose first bytes did not match their Content-Type. pixa does
-- not fetch such a URL again until its row expires.
CREATE TABLE IF NOT EXISTS negative_cache (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    source_host TEXT NOT NULL,
    source_path TEXT NOT NULL,
    source_query TEXT NOT NULL DEFAULT '',
    expires_at DATETIME NOT NULL,
    UNIQUE(source_host, source_path, source_query)
);
CREATE INDEX IF NOT EXISTS idx_negative_cache_expires ON negative_cache(expires_at);

-- Cache statistics for monitoring
CREATE TABLE IF NOT EXISTS cache_stats (
    id INTEGER PRIMARY KEY CHECK (id = 1),
    hit_count INTEGER NOT NULL DEFAULT 0,
    miss_count INTEGER NOT NULL DEFAULT 0,
    upstream_fetch_count INTEGER NOT NULL DEFAULT 0,
    upstream_fetch_bytes INTEGER NOT NULL DEFAULT 0,
    transform_count INTEGER NOT NULL DEFAULT 0,
    last_updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
);
INSERT OR IGNORE INTO cache_stats (id) VALUES (1);

-- A random value that a login session carries from its login. pixa makes it
-- when the table has no row, and each logout replaces it; a login session
-- carrying another value is refused, so logging out ends every login session.
CREATE TABLE IF NOT EXISTS logout (
    id INTEGER PRIMARY KEY CHECK (id = 1),
    logout_value TEXT NOT NULL
);