-- Step 1: Create the member_states lookup table
CREATE TABLE member_states (
    state_code CHAR(1) PRIMARY KEY,
    state_name VARCHAR(20) NOT NULL,
    description TEXT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Insert the three states
INSERT INTO member_states (state_code, state_name, description) VALUES
('A', 'Active', 'Member is currently active'),
('I', 'Inactive', 'Member is temporarily inactive'),
('D', 'Deactivated', 'Member has been permanently deactivated');

-- Step 2: Create the member_state_log table
CREATE TABLE member_state_log (
    log_id SERIAL PRIMARY KEY,
    member_id INTEGER NOT NULL,
    state_code CHAR(1) NOT NULL,
    changed_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    changed_by INTEGER, -- Optional: user ID who made the change
    reason TEXT, -- Optional: reason for state change
    FOREIGN KEY (member_id) REFERENCES members(member_id),
    FOREIGN KEY (state_code) REFERENCES member_states(state_code)
);

-- Create indexes for better performance
CREATE INDEX idx_member_state_log_member_id ON member_state_log(member_id);
CREATE INDEX idx_member_state_log_changed_at ON member_state_log(changed_at);
CREATE INDEX idx_member_state_log_state_code ON member_state_log(state_code);

-- Step 3: Migration script to populate the log table from existing data
INSERT INTO member_state_log (member_id, state_code, changed_at)
SELECT 
    member_id,
    CASE 
        WHEN member_active = true THEN 'A'
        ELSE 'I'
    END,
    COALESCE(updated_at, created_at, CURRENT_TIMESTAMP)
FROM members;

-- Step 4: Create a view to get current member states (most recent log entry per member)
CREATE OR REPLACE VIEW member_current_state AS
SELECT DISTINCT ON (msl.member_id)
    msl.member_id,
    msl.state_code,
    ms.state_name,
    ms.description,
    msl.changed_at,
    msl.changed_by,
    msl.reason
FROM member_state_log msl
JOIN member_states ms ON msl.state_code = ms.state_code
ORDER BY msl.member_id, msl.changed_at DESC, msl.log_id DESC;

-- Step 5: Function to change member state (ensures proper logging)
CREATE OR REPLACE FUNCTION change_member_state(
    p_member_id INTEGER,
    p_new_state_code CHAR(1),
    p_changed_by INTEGER DEFAULT NULL,
    p_reason TEXT DEFAULT NULL
) RETURNS VOID AS $$
BEGIN
    -- Validate that the state exists
    IF NOT EXISTS (SELECT 1 FROM member_states WHERE state_code = p_new_state_code) THEN
        RAISE EXCEPTION 'Invalid state code: %', p_new_state_code;
    END IF;
    
    -- Validate that the member exists
    IF NOT EXISTS (SELECT 1 FROM members WHERE member_id = p_member_id) THEN
        RAISE EXCEPTION 'Member not found: %', p_member_id;
    END IF;
    
    -- Insert the new state log entry
    INSERT INTO member_state_log (member_id, state_code, changed_by, reason)
    VALUES (p_member_id, p_new_state_code, p_changed_by, p_reason);
END;
$$ LANGUAGE plpgsql;

-- Step 6: Common queries you'll need

-- Get all active members
SELECT m.*, mcs.state_name, mcs.changed_at as last_state_change
FROM members m
JOIN member_current_state mcs ON m.member_id = mcs.member_id
WHERE mcs.state_code = 'A';

-- Get member state history
SELECT 
    msl.changed_at,
    ms.state_name,
    msl.reason,
    msl.changed_by
FROM member_state_log msl
JOIN member_states ms ON msl.state_code = ms.state_code
WHERE msl.member_id = 123 -- Replace with actual member_id
ORDER BY msl.changed_at DESC;

-- Count members by state
SELECT 
    ms.state_name,
    COUNT(*) as member_count
FROM member_current_state mcs
JOIN member_states ms ON mcs.state_code = ms.state_code
GROUP BY ms.state_code, ms.state_name
ORDER BY ms.state_code;

-- Step 7: Example usage of the change_member_state function
-- Change member 123 to inactive
SELECT change_member_state(123, 'I', 1, 'Member requested temporary suspension');

-- Reactivate member 123
SELECT change_member_state(123, 'A', 1, 'Member reactivation approved');

-- Step 8: After testing, remove the old column (CAREFUL!)
-- ALTER TABLE members DROP COLUMN member_active;